Method of producing hardboard in prdetermined shapes and a mat used in such method



Feb. 4, 1964 c. BOJANOWSKI 3,120,466

METHOD OF PRODUCING HARDBOARD IN PREDETERMINED SHAPES AND A MAT USED INSUCH METHOD Filed March 21, 1960 FEED DIRECTION I IIIIIIIIIIIIIIII/IIIIIIIIIIIIII A W M m 02%" Attorney United States Patent 3,12ll,466METHGD 0F PRGDUCENG HARDBUARD IN PRE- DETERl /HNED SHAPES AND A MAT USEDIN SUCH METHQD Carl Bojanowsld, Alpena, Mich, assignor to Abitibi Power3: Paper tlompany, Limited, Iroquois Falls, @utar-lo, Qanada Filed Mar.21, 19%, Ser. No. 16,346 (Zlaims. (ill. 162-164) This invention relatesto a method for making hardboard in predetermined shapes and to a matused in such method.

The utilization of hardboard has been limited by the fact that whenconventional manufacturing techniques are used the product is in theform at a flat sheet or can be slightly curved. While there are severalmethods of obtaining irregular three dimensional shaped hardboard, noneappear to be totally satisfactory. For example if the conventional wetprocess is used comprising the delibration and refining of wood chipsfollowed by forming and dewater-in g the wet lap on a Fourdriniermachine and the consolidation of the dewatered Wet lap under heat andpressure, it is possible to impart a slight curvature or minorindentations to the hardboard by using suitably shaped platens in thehot press, but if an attempt is made to use platens shaped to give asevere draw, the hardbourd will be severely weakened or rupture.

The methods which have previously been considered for making shapedhardboard have mainly been based on the idea of preforming the met. Inaccordance with one technique a wet slurry is deposited on a formapproximating the end shape and dried on this form. The ast mentionedmethod suffers from the disadvantage that the shaped mat does not retainits preformed shaped unless handled with extreme care with theconsequence that it is impractical to ship the preformed mat to afabricator. The preformed mat must be specially made to suit thecontemplated end product, consequently the method is both costly andsubject to handling problems. Some shapes have been made by acentrifugal forming technique in accordance with which a sluary isforced against a screen having the desired shape by centrifugal action,following which heat and pressure are applied undcr conditions whichproduce some hardening though not sufiicient to compare to usualhardboard standards. The latter tecimique is costly and the product isre only for limited applications.

it is believed that air felting and also a semi dry Pour- .dririier typeformation have been tried in an attempt to produce a mat having greaterdraw than conventional techniques, but without being able to provide amat which can readily be handled and which at the same time providessatisfactory elongation when pressed in forming dies.

An object of this invention is to provide amat which has superiorelongation compared with the mat made by conventional techniques so asto be suitable for making a wider range of shaped products than ispossible using conventional hardboard techniques A further object ofthis invention is to provide amat which can readily be shaped to conformwith dies in which the mat is to be moulded into hardboard.

Anotherobjeotof this invention is to provide a mat which canconveniently be shipped.

in accordance with this invention a dry mat is formed and this in itsbroadest aspect is fiexibilized by a crushing operation, to break downthe fibre bond in the mat. This crushing operation makes the mat moreflexible and improves the elongation of the board in a die to a modestextent to provide a mat suitable for pressing shapes which vary to aminor extent from the flat plane. The crushing ice operation can belocalized if desired to the portion or portions of the mat which will beelongated in the die.

Greatly improved results are obtained by both crush ing and bendin thedry mat so as not only partially to break down the fibre bond in the matbut also to provide cleavage planes extending primarily parallel to thesurface of the mat, thus forming laminae extending substantiallyparallel to the surface of the mat and being adhered togethersuffioiently loosely at the cleavage planes to perrnit relative slidingmovement between the laminae.

The crushing and bending operations can be performed simultaneously orthe bending operation can follow the crushin g operation.

The crushing operation can be performed by compressing the entire mat orthe entire portion of the mat to be ilexibilized at once, for example ina press or by pounding the mat, but it is best successively to applypressure to areas of the board extending in one direction such as by theuse of rollers as the latter technique gives better working of the matthan compressing the entire mat atoncc Where rollers or the like areused, it is best to pass the mat through the rollers first in onedirection and then in a direction transverse to the first direction toprovide a mat having uniform elongation in each direction.

The bending operation may be carried out in one direction particularlyif the shape to be formed requires good elongation in one direction onlybut the best results and the most versatile mat is obtained by bendingfirst in one direction and then in a direction transverse to the firstdirection. The bending operation or operations should be carried out soas to produce the desired cleavage planes without rupturing the mattransversely to the direction of bending.

Where rollers or the like are used to provide directional crushing intwo directions, and the mat is also subjected to a bending operation intwo directions, the sequence of operations can be crushing in onedirection followed or accompanied by bending in that direction and thencrushing in a direction transverse to the first direction followed oraccompanied by bending in the transverse direction. An alternativesequence is crushing first in one direction and then transverselyfollowed by bending in one of such directions, followed by bending inthe other of such directions. Another alternative sequence is crushingin one direction followed by bending in each of transverse directions,and then crushing in a direction transverse to the first direction.

The method of this invention significantly increases the capacity of themat to conform to the shape of a die and to elongate in the pressWithout rupturing so as to greatly increase the range of shaped productsthat cm be formed. The additional flexibility of the mat also isadvantageous in that th mat will conform with a curved die.

Referring now to the drawings which illustrate a method in accordancewith this invention.

FIGURE 1 is a diagrammatic elevation view showing an apparatus suitablefor use in the process of the invention for providing a crushingoperation and illustrating also the lines of force and the resultantcleavage planes.

FIGURE 2 is an elevation view similar to FEGU'RE 1 but illustrating thecrushing and bending operation.

FIGURE 3 is a perspective view of a die formed sheet of hardboard.

FIGURE 4 is a section view on the line IVIV of FIGURE 3.

The mat which is to be fiexibilized may be prepared from afibrous wetlap produced by the defibration and refining of wood chips, followed byforming and dewatering on a forming machine such as a Fourdrinier, byconventional hardboard methods to provide a lignocellulosic fibre Wetlap. However, it is desirable that an integral binder be used. Theamount and type f binder depends on the particular molding required. Asuitable binder may be one or a combination of materials selected from awide range of binders including thermosetting resins such as phenolformaldehyde and melamine formaldehyde, thermoplastic resins such asasphalt, the resin known under the trade name Vinsol and manufactured byHercules Powder Co., which is a thermoplastic resin derived from pinewood and containing phenol, aldehyde and ether groups, and wood resins,petroleum hydrocarbons such as the material known under the trade namePiccopale, and manufactured by Pennsylvania industrial Chemical Co.,drying oils of vegetable, animal, or pctroleurn origin such as linseedoi tung oil, safilower oil and latices such as styrene-butadiene andpoly-vinylacetate. It is best to use a combination of binders to achievegood forming characteristics and also good physical properties in thefinished board. Thermoplastic resins have an excellent plasticizingeffect in the hot forming press and permit severe draws without ruptureof the mat. Drying oils, thermosetting resins and most latices tend toproduce the best strength and water resistance. The amount of binderused will vary according to the choice of binder and the particularmolding required, but will normally be within the range of 1 to 25% byweight of the dry mat and is preferably within the range of 4% to 10%.

Overlays of paper, cloth, plastic or the like may be used provided thatsuch overlays are suificiently extensible not to rupture in the die.Although it is preferred for most applications that an integral binderbe employed, it is not essential for all purposes and some formed shapesmay require high strength only in particular areas and the binder can beapplied by a localized spraying of an aqueous or solvent solution ofbinder on the forming mat in the particular areas where greater strengthis required. The binder could also be applied with a brush or in anyother convenient manner. The spray application may be to the wet lap,the dried mat or the crushed mat prior to hot pressing.

The mat to be fiexibilized in accordance with this invention should bedried to the state at which it stiffens and becomes relatively rigid, sothat the crushing and bending operations will produce the desiredpartial break down of the fibre bond, preferably accompanied by theformation of cleavage planes. The density at this stage will varybetween 12 and 40 lbs. per cubic foot, with a typical density being 20lbs. per cubic foot. The moisture will be below 10% and preferably 0.1to 2%. If a mat produced by the wet process of making hardboard, has Inot been dried to a sufficient extent for the fibres to be bonded, theindividual fibres will tend to conform with the crushing and bendingwithout producing the desired breakdown of the fibre for the formationof cleavage planes. Furthermore, there may be a tendency of the mats toblow in the press if the moisture content is above 2%. Where an integralbinder is used the wet mat should be dried under conditions of time andtemperature varying with the binder such that the binding potential isnot developed to an extent such as to prevent the desired partialbreakdown of the fibre bond on formation of cleavage planes fromoccurring. Where the binder is thermosetting, premature loss of thebinding potential during drying should be avoided.

The dried mat is then subjected to a crushing operation and preferablyalso to a bending operation. FIGURE 1 illustrates a method ofaccomplishing the crushing operation, and what are understood to be themain forces involved in the method illustrated. However, the forces andstresses which arise are complex. The predominant stresses may vary inmethods in accordance with this invention. It is not desired thereforethat this invention be taken as being limited by a particulartheoretical explanation.

In FIGURE 1 guide rolls 1t) and 11 feed dry mat 12 through crushingrolls 13 and 14 which may, for example. have a nip pressure of 10 to 15pounds per square inch, for a typical 20 lbs. per cubic foot mat. Rolls13 and 14 may for example be 6" in diameter for treating a dry mat whichis /2" in thickness. Guide rolls 15 and 16 support the crushed mat.Tension lengthwise of the mat will be created at the nip of rolls 13 and14. This tension will be greater adjacent to the surface of the mat asindicated by arrows 17 than in the centre of the mat as indicated byarows 18 to create shear forces within the crushed mat 2t)". These shearforces break down the natural fibre bond in the mat.

In FIGURE 2 a bending roll 19 is located at the nip exit of rolls 13 and14. This bending roll together with guide rolls 15a and 16.1 are offsetfrom the plane of dry mat 12 to provide a reverse bend which causes theformation of cleavage planes. The tension at the nip close to thatsurface of the mat which is adjacent to roll 19, will be increased incomparison with FIGURE 1 as indicated by the arrow 17a and this will beaccompanied by a decrease in the tension at the opposite surface asindicated by the arrow 17b. When the board is bent back by the action ofbending roll 19 and guide rolls 15a and 16:1, there will be tension asindicated by arrows 21 at the surface of the mat which is close to guiderolls 15a and 16a accompanied by compression as shown by arrow 22 closeto bending roll 19. Bending the mat thus gives rise to additional shearforces within the mat to form cleavage planes. The cleavage planes incrushed mat 20a in FIGURE 2 are designated 23a. Crushing rolls 13 and 14may for example have a nip pressure of 10 to 15 pounds per square inchfor a typical 20 lbs. per cubic foot mat. Rolls 13, 14 and 19 may forexample be 6" in diameter for treating a dry mat which is /z" inthickness. Roll 19 is located so that the angle of bend will besufficient to create the cleavage planes to the desired extent withouthowever, being so great as to cause rupturing or tearing of the dry matin a direction perpendicular to its surface. The angle of bend 0 inFIGURE 2 will be the angle subtended by a line 24 drawn parallel to thesurfaces of the dry mat and a line 25 passing mid way between rolls 13and 14 and rolls 19 and 15a respectively (where roll 15a is opposite toroll 19). The best angle of bend 0 will vary but will be about 5 to 20for a mat of /2" thickness. The spacing between rolls 13 and 19 shouldbe sufiicient for the bending not to be unduly abrupt so as to avoidrupturing the mat. Thus where the rolls are 6 in diameter an appropriatespacing of the centres of rolls 13 and 19 would be about 18".

A single fiexibilizing operation consisting of crushing and bending asdescribed above in one direction only, will improve the capacity of thedry mat to elongate in a die press. However, a considerable improvementin the results obtained and greatly increased flexibility in the shapeswhich can be produced is obtained by subjecting the dry mat to a secondfiexibilizing operation in a direction transverse to that of the firstoperation. Thus, if the first crushing and bending operation is alongthe length, the second crushing and bending operation will be across thelength. It is preferred that the first operation be along the grain andthat the second operation be across the grain as the sequence is lesslikely to cause rupturing than if the reverse sequence were followed,but either sequence may be used. Alternatively each of the bendingoperations may be in other directions. Repeated rolling with increasednip pressure and increased flexing angles may be desired for someproducts.

In the subsequent bending operations, the angle of bending should bechosen which will give increased cleavage planes without causing tearingor rupturing.

The flexible product resulting from the second bending operation isflexible in each direction and resembles a thick floor carpeting. Itdiffers from the initial dry mat in that it has cleavage planesgenerally parallel to the surfaces of the mat. In addition, it iscapable of elongation in a die press to the extent of about 30% to 60%.The normal range of thickness for the mat will be about inch to 2inches.

The fiexibilized dry mat is placed in a die press and subjected to presscycles, such as at temperatures 300 to 500 F., and a pressure of about400 to 2,000 p.s.i., and cycle times of seconds to 10 minutes. A typicalpress cycle for mat containing 2% drying oil and 2% Vinsol is 450 F.,1,200 p.s.i. pressure for 1 minute.

Another typical press cycle for mat containing 2 /2% phenolic resin and2 /2 petroleum resin is 400 F., 600 p.s.i. and 3 minutes.

At high temperatures moisture in the mat may cause blistering and it maybe necessary to dry the mat to a low moisture content or to insert aflexible wire screen into the die on one side of the mat to allowmoisture to escape.

If desired the properties of the board can be enhanced in a conventionalmanner by post baking in an oven or by hot stacking.

FIGURES 3 and 4 are illustrative of the shapes that can be produced inaccordance with this invention. In FIGURES 3 and 4'there is illustrateda hardboard sheet 26 shaped'in a die press to have an indentation 27.The production of the shape illustrated in FIGURES 3 and 4 involve theuse of a heated platen forming die with a 30% draw.

The process of this invention is further exemplified by the followingexample:

Example A dry mat having a density of lbs. per cubic foot, a thicknessof inch and a moisture content of about 5% is made with the inclusion of2%% of linseed oil and 2 /2% petroleum hydrocarbon. The mat is rolledalong its length between crushing rolls having a nip pressure of about12 lbs. per square inch using the apparatus illustrated in FIGURE 2,with 6" diameter bending and crushing rolls, at an angle of bend of 10and with the bending roll and closet crushing rolls spaced 18". The matis rolled transverse to its length using the same apparatus and nippressure. The mat is then dried to below 1% in moisture. The mat is thenmolded at 450 F., and 1,200 p.s.i. using a press cycle of 45 seconds toform an automotive door panel.

I claim:

1. A method of making a shaped sheet of hardboard comprising crushing amat of wood fibres bonded together and having a moisture content ofbelow 10% to provide a partial breakdown of the fibrous bond and providea mat having increased flexibility and elongation, and then die formingthe mat with heat and pressure to make a shaped sheet of hardboard.

2. A method of making a shaped sheet of hardboard comprising subjectinga mat of wood fibres bonded together and having a moisture content ofbelow 10% to a crushing operation involving the successive applicationof pressure to areas of the surface of the mat extending in onedirection followed by a second crushing operation involving thesuccessive application of pressure to areas of the surface of the matextending in a direction transverse to said one direction to provide apartial breakdown of the fibrous bond and provide a mat having increasedflexibility and elongation and then die forming the mat with heat andpressure to make a shaped sheet of hardboard.

3. A method of making a shaped sheet of hardboard comprising subjectinga mat of wood fibres bonded to ether and having a moisture content ofbelow 10 to a crushing operation to provide a partial breakdown of thefibrous bond and bending said mat without rupturing the mat to provide aflexible mat of increased elongation and with cleavage planes generallyparallel to the surface of the mat, and then die forming the mat withheat and pressure to make a shaped sheet of hardboard.

4. A method of making a shaped sheet of hardboard comprising forming amat of wood fibres bonded together having a moisture content of about0.1 to 2%,and including an integral binder in the amount of about 1 to25%, said integral binder having binding potential, subjecting said matto a crushing operation to provide a partial breakdown of thefibrous-bond and bending said mat without rupturing the mat to provide aflexible mat of mcreased elongation comprising lamellae separated bycleavage planes extending generally parallel to the surface of the matand then die forming the mat with heat and pressure to make a shapedsheet of hardboard and develop the binding potential of said binder.

5. A method of making a shaped sheet of hardboard comprising the stepsof forming a ligno-cellulosic fibre wet lap, de-wiatering and dryingsaid wet lap to form a stiff mat having a moisture content of below 10%,crushing said mat by the successive application of pressure to areas ofthe mat extending in one direction to provide a flexible mat Withouttearing said mat and then subjecting said mat to heat and pressure toform a shaped sheet of hardboard.

6. A method of making a shaped sheet of hardboard comprising the stepsof forming a ligno cellulosic fibre wet lap containing an integralbinder, dewatering and drying said wet lap to form a stiff mat having amoisture content of below 10% under conditions of time and temperatureat which said binder retains binding potential for bonding said sheets,crushing by the successive application of pressure to areas of the matextending in one direction without tearing said mat and then subjectingsaid mat to heat and pressure to form a shaped sheet of hard'ooard, andsetting said binder at a stage not earlier than the application of saidheat and pressure.

7. A method of making a shaped sheet of hardboard comprising the stepsof forming a ligno-cellulosic fibre wet lap containing an integralbinder, dewatering and drying said Wet lap to form a stiff mat having amoisture content of below 10% for a time and at a temperature at whichsaid binder retains binding potential for bond ing said sheets, crush ngsaid mat by the successive application of pressure to areas Olf theboard extending in one direction, crushing said mat by the successiveapplication of pressure to areas of the board extending in a directiontransverse to the direction of the first operation Without tearing saidmat and then subjecting said mat to heat and pressure to form a shapedsheet of hardboard, and setting said binder at a stage not earlier thanthe application of said heat and pressure.

8. A method of making a shaped sheet of hardboard comprising the stepsof forming a ligno-ceilulosic fibre wet lap containing an integnallbinder, dewatering and drying said wet lap to form a stiff mat having amoisture content of below 10% for a time and at a temperature at whichsaid binder retains binding potential for bonding said sheets, crushingby the successive application of pressure to areas of the mat extendingin one direction of said mat and bending the crushed mat to providecleavage planes generaliy parallel to the surface of said mat with outtearing said mat and then subjecting said mat to heat and pressure toform a shaped sheet of hardboard, and setting said binder at a stage notearlier than the application of said heat and pressure.

9. A method of making a shaped sheet of hardboard comprising the stepsof forming a ligno-cellulosic fibre wet lap containing an integralbinder, ,dewatering and drying said wet lap to form a stiff mat having amoisture content of below 10% for a time and at a temperature at whichsaid binder retains binding potential for bonding said sheets, crushingsaid mat by the successive application of pressure to areas of the matextending in one direction, and bending the crushed mat to providecleavage planes generally parallel to the surface of said mat withouttearing said mart, crushing said mat by the successive application ofpressure to areas of the mat extending in a direction transverse to thedirection of the first operation, and bending the crushed mat to provideadditional cleavage planes generally parallel to the surface of said matwithout tearing said mat and then subjecting said mat to heat andpressure to form a shaped sheet of hardboard, and setting said binder ata stage not earlier than the application of said heat and pressure.

10. A method as in claim 9 in which said binder is a combination ofthermo-plastic and thermosetting resins.

11. A method as in claim 9 in which the moisture of the dry mat is from0.1 to 2%.

12. A method of making a shaped sheet of hardboard comprising the stepsof forming a ligno-cellulosic fibre wet lap containing an integralbinder, dewatering and drying said wet lap to form a stiff mat having amoisture content of below 10% for a time and at a temperature at whichsaid binder retains binding potential for bonding said sheets, crushingsaid mat partially to rupture fibrous bonds in said mat, bendingsuccessive areas to the mat extending in one direction to providecleavage planes generally parallel to the surface of the mat Withouttearing said mat, bending successive areas of the mat extending in adirection transverse to said one direction to pro vide additionalcleavage planes generally parallel to the surface of the mat withouttearing the mat and subjecting the mat to heat and pressure to provide ashaped sheet of hardboard and setting said binder at a stage not earlierthan the application of heat and pressure.

13. A mat adapted to be consolidated under heat and pressure in aforming die to provide shamd hardboard comprising a dry flexible fibrousmat of defibrated wood chips fc-rrned from laminae separated by cleavageplanes generally parallel to the surface of the mat when made by amethod comprising the stages of subjecting a mat of wood fibers bondedtogether and having a moisture content below 10% to a crushing operationto provide a partial breakdown of the fibrous bond and bending said matwithout rupturing the mat.

14. A mat as in claim 13 comprising an integral binder having bindingpotential and being in an amount of l to 25%.

15. A mat as in claim 13 in which said mat has an elongation of at leastin said forming die.

References Cited in the file of this patent UNITED STATES PATENTS107,562 Taylor et a1. Sept. 20, 1870 216,108 Scott June 3, 1879 327,138Churchill Sept. 29, 1885 860,696 Scherf July 23, 1907 1,900,698 EllisMar. 7, 1933 2,229,401 Worm Jan. 21, 1941 2,907,071 Meiler et al. Oct.6, 1959

9. A METHOD OF MAKING A SHAPED SHEET OF HARDBOARD COMPRISING THE STEPSOF FORMING A LIGNO-CELLULOSIC FIBRE WET LAP CONTAINING AN INTEGRALBINDER, DEWATERING AND DRYING SAID WET LAP TO FORM A SSTIFF MAT HAVING AMOISTURE CONTENT OF BELOW 10% FOR A TIME AND AT A TEMPERATURE AT WHICHSAID BINDER RETAINS BINDING POTENTIAL FOR BONDING SAID SHEETS, CRUSHINGSAID MAT BY THE SUCCESSIVE APPLICATION OF PRESSURE TO AREAS OF THE MATEXTENDING IN ONE DIRECTION, AND BENDING THE CRUSHED MAT TO PROVIDECLEAVAGE PLANES GENERALLY PARALLEL TO THE SURFACE OF SAID MAT WITHOUTTEARING SAID MAT, CRUSHING SAID MAT BY THE SUCCESSSIVE APPLICATION OFPRESSURE TO AREAS OF THE MAT EXTENDING IN A DIRECTION TRNSVERSE TO THEDIRECTION OF THE FIRST OPERATION, AND BENDING THE CRUSHED MAT TO PROVIDEADDITIONAL CLEVAGE PLANES GENERALLY PARALLEL TO THE SURFACE OF SAID MATWITHOUT TEARING SAID MAT AND THEN SUBJECTING SAID MAT WITHOUT TEARINGSAID MAT AND THEN SUBJECTING SAID MAT TO HEAT AND PRESSURE TO FORM ASHAPED SHEET OF HARDBOARD, AND SETTING SIAD BINDER AT A STAGE NOTEARLIER THAN THE APPLICATION OF SAID HEAT AND PRESSURE.